The United Nations is appealing for $109m to finance this year's relief operations in the vast East African country of Sudan.

Officials have said that failure to raise the money will severely compromise efforts to provide humanitarian aid to four million people suffering the effects of war and famine.

Further fighting and bad weather will create even greater hardship, they said.

The BBC's East Africa correspondent reports that donor fatigue has already led to cutbacks for the UN's longest-running air relief operation.

Last year, donor countries were asked for $120m. They gave just 40% of the target.

The World Food Programme and the children's aid fund Unicef said that has made this year's aid all the more urgent.

Aid has been airlifted to Sudan ever since the 1988 famine

Since the Sudanese famine of 1988, the two agencies and nearly 40 aid organisations have been flying mercy missions under the name Operation Lifeline Sudan (OLS) into government and rebel-held areas.

Carl Tintsman, the chief co-ordinator for OLS, said that the people of Sudan were in desperate need of help. "It is a dire, life-threatening situation. Unless we get the money we honestly don't know what their fate will be."

Mr Tintsman also said that aid organisations were expecting an
increase this year in fighting between Muslim government forces in the north and the black African population of the south, who are mainly Christian or animist.

In the last two weeks, the relief operation has been hampered by a government veto of the air-bridge to the south-western province of Bahr El Ghazal. It has been reported that more than 150,000 people there have been displaced by recent fighting.

Since 1983 more than one million people have been killed in the civil war that has devastated the Sudanese economy and costs the government an estimated $1.5m a day.